Chevrolet DB90 Series, Service Manual

Page: 133 / 242

Sec. 6Y-127
A. C. GENERATING SYSTEM (NON-INTEGRAL TYPE)
GENERATOR DRIVE BELT
TENSION ADJUSTMENT
CAUTION: When adjusting drive belt
tension, apply p ressu re at center of gen­
erator and never against either end fram e.
D rive b elts m ust be kept at proper tension. A
lo o se or broken b elt w ill affect operation of the
generator. A drive belt that is too tight w ill place
e x c e s s iv e strain on bearin gs.
A ll generators are p iv o t-b a se mounted. To
adjust drive belt ten sion , loosen the adjustment
arm clam p bolt and generator to mounting bracket
or support bracket pivot bolt, and move generator
to obtain recom m ended tension.
V -B e lt Tension
G enerator drive belt tension on v e h ic le s equip­
ped with V -b elts should be adjusted to 120-130
pounds on new b e lts, u sin g belt tension gauge (J-
23600). U sed drive b elts should be adjusted to 80-
90 pounds. P la c e gauge at center of g rea test belt
span when adjusting drive belt tension.
NOTE: On a new v e h ic le , or after having in­
sta lle d a new drive b elt, check tension tw ice in
fir s t 200 m iles of operation. R efer to ENGINE
COOLING SYSTEM (SEC. 6K) for d rive b elt r e ­
placem ent.
IMPORTANT: When replacing dual drive b elts,
it is e sse n tia l that the en tire s e t be replaced at the
sa m e tim e. B e lts are availab le in m atched se ts
only.
P o ly -V B elt Tension
G enerator drive b elt tension on v e h ic le s equip­
ped with P oly-V b elts should be adjusted using
(J-23586) b elt tension gauge. Gauge should be
placed at center of lo n g est b elt span to obtain
proper reading. When adjusting a new drive belt,
adjust tension to "NEW” belt sp ecification , turn
engine over se v e r a l tim e s, then r e se t belt tension
to "NEW" b elt sp ecifica tio n .
NOTE: A P o ly -V b elt is considered USED
after one hour's operation or approxim ately 50
m ile s driving tim e. R efer to ENGINE COOLING
SYSTEM (SEC. 6K) for drive belt replacem ent.
G enerator drive b elt ten sion on v e h ic le s equip­
ped with the 6-71 D ie s e l engine and P o ly -V drive
belt should be adjusted to 4 4 -5 4 pounds on a new
b elt u sing (J-23586) belt ten sion gauge. U sed b elts
should be adjusted to 29-39 pounds.
G enerator drive belt tension on v e h ic le s equip­
ped w ith the 8V-71 D ie s e l engine and P o ly -V drive
belt should be adjusted to 84-94 pounds on a new
b elt or 64-74 pounds on a used b elt.
GENERATING SYSTEM TROUBLE
SYMPTOMS
Abnormal operation of the charging sy stem
w ill u sually be indicated by one or m ore of the
follow ing conditions:
1. Faulty indicator lamp operation (ste e l tilt
cab m odels only).
a. F ailu re of indicator lamp to illum inate when
ignition or control sw itch is turned on with engine
not running.
b. Indicator lamp continues to glow with engine
running.
c. Indicator lamp fa ils to go out when ignition
o r control sw itch is turned off.
2. B attery undercharged (low sp ecific gravity
of electr o ly te).
3. B attery overcharged as evidenced by e x ­
c e s s iv e w ater u sage indicating an extrem ely high
charging rate.
4. A m m eter show s a high charging rate with
a fully charged battery.
5. A m m eter show s a low or n o-ch arge with a
p artially discharged battery.
GENERATOR ON VEHICLE TEST
The follow ing is a lis t of the m ost common
generator d efects encountered:
1. Open or shorted generator diodes.
2. Open, shorted, or grounded stator winding.
3. Open, shorted, or grounded field winding.
4. Worn generator b ru sh es.
5. E x c e s s iv e generator n o ise.
G enerator diodes and stator windings should
be checked a s explained under "Generator Output
T e s t” la te r in this se ctio n . If a defect is indicated
by th is te st, rem ove the generator and rep air.
G enerator field windings and b ru sh es should
be checked a s outlined under "Charging System
Trouble A n a ly sis Chart” la te r in th is sectio n . If
th is check indicates a defect in the field winding,
rem ove the generator and rep air. R eplace worn
b ru sh es a s explained under "Generator B rush R e ­
p lacem ent" la te r in this section .
E x c e ssiv e generator n o ise is usually the r e ­
su lt of one or m ore of the following:
1. B rush "Squeal" caused by a hard spot on
one of the brushes o r rough or dirty slip r in g s.
2. Dry or rough b earings in generator end
fram e.
IMPORTANT: Dry or rough b earin gs may be
the resu lt of over-tigh ten in g generator drive b elt,
lo o s e generator mountings, or an unbalanced gen­
erator fan or p u lley. R em ove generator and rep air.
3. A d efective diode or stator resulting in an
e le c tr ic a l unbalance.
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL SUPPLEMENT